Electronic vacuum tube system



Sept 28, 1937. H. o' r 7 2,094,101

ELECTRONIC VACUUM TUBE SYSTEM Filed April 25, 1927.

FIE 2 INVENTOR w /aro/d E 5/0679 Hi5 AT TGRNEY Patented Sept. 28, 1937 UNITE stares eAreT OFFICE ELECTRONIC VACUUM TUBE SYSTEM aware Application April 23, 1927, Serial No. 186,039

3 Claims.

This invention relates to vacuum tubes that operate to modify the character or strength, or both, of electrical impulses, and more particularly to the manner in which such vacuum tubes 5 are supplied with the necessary electrical energy for causing them to function in the desired manner.

Such vacuum tubes, usually called audions, are utilized extensively in connection with reception and transmission of radio signals. In such uses, they are commonly connected in tandem relation for successive amplification, and in the case of reception, for detection. Each tube includes a source of electronic emission, such as a heated filament, from which the electrons fiow to a plate or anode. This plate must be kept at a potential positive with respect to the filament in order to attract the electrons. Furthermore, current must be supplied to the filament to heat it to an operating temperature. The space current formed by the flow of electrons is found to be greatly affected by potential conditions in the path; and for creating large variations in the space current, it is now common to provide a control electrode. The degree and sense of variation depends upon the relative potentials of the control electrode and filament. It is due to this phenomenon that amplification and other effects can be obtained by the aid of the tube.

It is one of the objects of my invention to make it possible to supply the necessary potentials to the plates of a plurality of tubes in a simple manner.

It is another object of my invention to make it possible to supply both the filament heating current and the plate potentials from a common source, and in such manner that the plate potential for each tube is derived from a distinct portion of a series circuit.

45 to tube uses. It is another object of my invention to provide an improved form of battery eliminator.

In connection with radio receiving sets, it is now common to provide one or more stages of amplification operating on the received impulses before and after detection. It is desirable to ensure that the amplifier system will have the same.

amplification effect upon signaling currents of 5 any frequency within the range of reception.

In the usual form of receiving-set, use is made It is another object of my invention to provide an improved and simplified scheme for causing said amplification to be substantially constant within the range of operation.

My invention possesses many other advantages, and has other objects which may be made more 5 easily apparent from a consideration of several embodiments of my invention. For this purpose I have shown a few forms in the drawing accompanying and forming part of the present specification. I shall now proceed to describe these 10 forms in detail, which illustrate the general principles of my invention; but it is to be understood that this detailed descriptionis not to be taken in a limiting sense, since the scope of my invention is best defined by the appended claims. 15

Referring to the drawing: I

Figure l is a schematic wiring diagram showing one form of my invention; and

Fig. 2 is a similar diagram of a modification.-

In Fig. 1, I show a conventional type of absorbing circuit, including the elevated conductors II,

a loading coil l2 and a ground connection l3. The radiant energy received in this absorbing circuit is passed successively through a series of vacuum tube amplifiers, as well as a detector, and finally, in its amplified and detected state, is caused to affect a translating device M, such as a loud speaker or head phones. The scheme of interconnection of the electronic emission devices linking the translating device I4 and the pick-up system I il2-I3, can of course be varied to suit different conditions. In the present instance,

a cascade system is shown in which there are three stages of radio frequency amplification, a detector stage and two stages of audio frequency 5 amplification. The system as shown also includes a battery eliminator-l5, which has a positive output terminal [6 and a negative output terminal ll. It is supplied as by-a transformer l3 from a commercial source of alternating cur- 4O rent connecting to leads I9. 'Any desirable form of eliminator could be utilized, the present form being indicated in a diagrammatic manner only.

Referring in greater detail to the interconnection of the various electronic emission devices, the loading coil 12 of the pick-up system is shown as inductively coupled to. a tunable circuit 20, which includes the coupling coil 2| and a variable condenser 22. It is now well-understood that the potential difference or E. M. F. across the ,coil: 2! or condenser 22 is a maximum when the circuit'is in tune to the frequency of the impulses that it is desired to receive. The tuning is accomplished by variation of the condenser 22 in this instance; and it is due to this selective effect of tuning that it is possible to some extent to separate signals in accordance with the frequency of the currents carrying these signals.

The first stage of radio frequency amplification acts upon the E. M. F. produced by the impulses across the condenser 22, so as to amplify it. For this purpose the thermionic device 23 is utilized, which comprises an evacuated vessel containing a heated filament 24, a control electrode 25, and a plate or anode 26. The input electrodes 24 and 25 are connected to opposite terminals of the condenser 22, whereby variations in potential are obtained between the control electrode 25 and the cathode 24 in accordance with the received signals, and whereby the space current between the filament 24 and plate 26 is varied in accordance with the signals. The output circuit of the amplifier tube 23 includes plate 26, coil 21, impedance 28, and filament 24. The positive potential required to be impressed upon plate 26 in order that it may attract electrons from filament 24, is provided by impedance element 28, in which a current is caused to flow, as described hereinafter, whereby a potential drop is produced across coil 28. To enhance this effect, coil 28 is made of sufiiciently high resistance so as to produce the desired potential difference, and to impress a positive potential on'plate 26 with respect to filament 24.

In the present instance the impedance device 28 is shown as an iron cored inductance coil, but other types could as well be used. The radio frequency component of the output current can be bypassed around coil 28 and filament 24 by the aid of a circuit comprising a small condenser 29 and ground connections 3|] and 3|.

In the present instance I show a stabilizing circult to maintain the system free from parasitic oscillation. This stabilizing circuit extends from grid 25 to the upper terminal of coil 21, and includes a small capacity 32, and a coil 33 coupled to coil 21. The value of the capacity of the small condenser 32 and the value of the inductances 33 and 21 are so arranged that whatever electromotive force is produced across the terminals of coil 21, due to the capacity coupling between the grid 25 and plate 26, is substantially annulled by the electromotive force induced by coil 33 in coil 21, due to the capacity coupling 32. If the capacity 32 is exactly equal to the parasitic coupling between grid 25 and plate 26, then coil 33 should be exactly equal to coil 21, and these coils should be closely coupled. This principle of stabilization is now so well known that further elucidation is considered unnecessary.

In the present instance, the first amplifier stage just described is conductively coupled to the succeeding stage. This is accomplished by the addition of an inductance 34 in series with coils 33 and 21, and a variable condenser 35 bridging all three coils. The input circuit of the succeeding radio frequency amplifier tube 36 is connected respectively to the upper terminal of condenser 35 and to the common terminals of coils 21' and 33. The tube 36 is shown as enclosing the usual three electrodes: filament 31, grid 38 and plate 39. The output circuit is similar to the output circuit of tube 23 and includes the iron cored inductance coil 49, across which there is produced a comparatively high direct current potential difierence to provide the plate potential. The radio frequency currents are bypassed around coil 49 and filament 31 through a circuit including the small fixed condenser 4|, ground connections 42 and 30 and the condenser 29. A stabilizing circuit 4344 is also included and operates in the manner described in connection with the first stage.

The third stage of radio frequency amplification includes the vacuum tube 45. This tube is coupled to the preceding one in a manner entirely similar to the coupling disclosed in connection with the first two tubes; and furthermore, its operation is identical with those previously described. As before, the output circuit includes the high impedance 46 across which a large direct current potential difierence exists to supply the plate potential. The radio frequency component is bypassed by the aid of by-pass condenser 41 and ground connection 48.

The succeeding stage includes a detector tube 49, having in its input circuit the usual grid leak 50 and grid condenser 5|. In other respects the connections are similar to those of the amplifier tubes just described. The electrodes 52, 53 and 54, and impedance 55 serve substantially the same functions as in the amplifier tubes. The output circuit of the detector tube 49 includes a portion of the iron cored coil 56, which is paralleled by a bypass condenser 51. The filament 52 is connected to the right hand terminal of coil 46, whereby this filament is in series relation with other filaments in the preceding stages. The high frequency currents are bypassed around filament 52 and coil 55 by a circuit including the condenser 58, ground connections 59 and 48, and condenser 41.

An audio frequency amplifier tube 60 is provided, which acts upon the detected signals passing through the output circuit of tube 49. This amplifier tube includes the usual elements 6|, 62 and 63. The input circuit, connecting to electrodes El and 62 includes coils 56 and 64, the latter forming a continuation of the coil 56, whereby an autotransformer effect is obtained. The output circuit includes the primary 65 of an iron cored transformer 66, as well as the potential drop producing device 61. A fixed condenser 68 and ground connection 69 serve as in the other stages, to by-pass the audio frequency current around the coil 61.

A power amplifier stage is inductively coupled to the audio frequency amplifier stage just described. However, before proceeding to describe this power amplifier stage in detail, I shall now I proceed to an explanation of the manner in which the filament current and plate voltages are obtained for the tubes already described. The rectifier I5 is shown as being provided with the filtering arrangement comprising an inductance coil 10, and capacities 1|, whereby to some extent the fluctuations in the rectified direct current are smoothed out. The rectification is obtained by a two way valve 12 that is indicated merely in a diagrammatic manner. The anodes 13, 14 are connected to opposite sides of the secondary coil 15, coupled to the primary coil 16 of the rectifier transformer IS. The negative lead of the rectifier connects to a central point on the coil 15, and also between two equal condensers 11 and 18, bridging coil 15. The operation of such a rectifier is now well understood. Briefly it can be stated that when the upper terminal of coil 15 is positive, then current fiows from anode 13 to the common cathode 19. On the other hand, when the lower terminal of coil 15 is positive, current flows from the lower anode 14 to the common cathode 19. For both half-cycles, terminal |6 remains positive, and terminal |1 remains negaive.

The positive terminal I6 of rectifier I is connected to one terminal of coil 61 in the output circuit of audio frequency amplifier 68. The negative terminal II is connected to the left hand terminal of filament 24, of the first tube 23. A series circuit is thus formed including all of the filaments such as 24, 31, 52, [H as well as the loading devices 28, 48, 46, 55 and 61. Sufiicient resistance can be included in these loading devices to provide the necessary potential difference to operate the audion tubes. Ordinarily a drop of 40 or 45 volts can be obtained, and the drop across each filament can be about 5 volts. of the rectifier I5 can be made to fulfill these requirements by proper winding of coils I5 and I6. Furthermore, due to the use of the by-pass circuits formed by the fixed condensers and ground connections such as 29 and 38, the fiuctuations in the rectifier output are thereby materially reduced, and it is not necessary to provide coil I8 in the rectifier with a large inductance or to provide condensers II with very large capacities. For the arrangement shown, a 225 volt rectifier can conveniently be utilized.

The power amplifier tube 88 has the usual electrodes 8|, 82 and 83. The filament BI is heated by the aid of a transformer 84, supplied from a local source of power. Across the secondary winding of the transformer, a potentiometer resistance 85 is connected. The input circuit thus includes the coupling coil 86, a portion of a resistance 81, resistance I8I, by-pass condenser I82, and a tap point on resistance 85. The portion of resistance 81 included in the input circuit is variable so as to vary the negative bias on grid 82 in the well understood manner. The output circuit includes plate 83, the primary 88 of a transformer 89, rectifier l5, resistance 81, and a tap on resistance 85. It is thus seen that the total potential difference of rectifier I5 is impressed upon the output circuit of the amplifier tube 88. The amplifier tube is coupled to the translating device I4 by the aid of the transformer 89; its secondary 98 is shown as directly connected to the translating device I4.

The advantages of this system just disclosed are numerous. The series arrangement of the filaments and the potential difference producing devices insures a simplicity in wiring not otherwise obtainable. Furthermore, the coils 28, 48, 46, 55 and 6'! and their by-pass circuits serve to smooth out the rectifier current fluctuation.

In the modification of Fig. 2, the tubes 23, 36, 45, 49, 68 and 88 perform the same function as the similarly numbered tubes in Fig. l. The rectifier I5 is also similarly connected to the filaments and the plate circuits of these tubes. In this form of the invention, care is taken to insure that all signals of frequencies within the limits of operation are all amplified substantially to the same extent. For this purpose the coupling in the tubes is arranged in such a way that if some tubes are most efficient at the lower frequencies, other tubes are most efficient at the higher frequencies, whereby these tubes in combination produce substantially constant amplification effects for the whole range of frequencies.

Thus for example, the radio frequency amplifier tube 23 is coupled to the second stage tube 36 in a manner disclosed in Fig. 2 of my previously filed application, Serial No. 175,500 filed March 15, 1927. In that application, it is described how it is possible for one tube to have a capacity reaction on the input circuit of a succeeding tube by the aid of a pair of equal capacities 9|, 92; and

The total voltage coil 93, connected to the midpoint of a pair of equal coupled coils 94 and 95, to which coils is coupled the coil 96 of the succeeding stage of amplification. The amplifier stage including tube 23 is thus most efficient at the low frequency range. However, tube 36 is arranged so that its output circuit has an inductive reaction on the succeeding stage, the stabilizing circuits being arranged substantially the same as those in Fig. 1 except that a transformer is used in place of an autotransformer. Therefore this second stage is most efficient for higher frequencies. The next stage 45 is entirely similar to the first stage 23, and is again most eflicient at the low frequencies.

As described in my prior application, above referred to, the divided circuit in the output circuit of the amplifier tube 23 has a capacitive reaction due to the use of a pair of parallel circuits, dividing at the common terminal of coils 94 and 95 and including the equal capacities 9| and 92 in parallel, The path is completed through the ground connections 9'! and 98. It is possible so to arrange the constants of the condensers and coils in this parallel circuit, that Within the range of operation of the system, the effect upon the succeeding stage is capacitive; that is, the circuit just described is parallel resonant at a frequency below the range of frequencies which the system is designed to cover in operation. On the other hand, the tube 36, having an inductive reaction on the succeeding stage, has an output circuit that by itself would be resonant at a frequency materially higher than the highest frequency within the range of operation.

The principle of allocating certain stages to be most efiicient either at low or high frequencies can be applied to the audio frequency stages also, so that some stages are most efiicient at the lower audible frequencies, and the others at the higher audible frequencies. Thus detector 49 has an inductive reaction on amplifier 68, causing it to be most efficient at the higher range. The resonance value of the output circuit is above audibility. The tube 88 however, is caused to be eificient at the lower range, as by the provision of a condenser 99 across the coupling coil I88. The predominant period of the input for tube 88 is below the range of audible signals to be amplified, say about 10 cycles.

If desired, a portion of the potential drop across the impedances which are used for supplying the tubes with plate potential may be used for negatively biasing the grids of the tubes.

An example of such an arrangement is shown in connection with the grid circuit of audio frequency amplifier tube 68 in Figure 2. A suitably located tap I85 on impedance is employed negatively to bias the grid 62 of tube 68. By-pass condenser I84 serves to complete the return circuit for audio frequency currents in the gridfilament circuit and resistance I83 may be employed to prevent slight fluctuations in potential in coil 55 from being impressed on the grid. By-pass condenser I82 and resistance I8I in the grid circuit of the second audio amplifier serve a similar purpose with reference to tube 88.

I claim:

1. In a system of the character described, a series of electronic emission devices arranged in succession to act upon electrical signaling impulses, each of said devices having an electron emitting electrode and a plate electrode, and means for supplying a potential to the plate of each device that is positive with respect to the electron emitting device, comprising a rectifier for modifying commercial alternating current into rectified direct current, means connecting said rectifier in series with all of the plate electrodes and electron emitting electrodes, said connecting means including a potential drop producing device between each plate electrode and its electron emitting electrode, said drop producing devices being inductive to assist in reducing fluctuation in the series circuit, and capacitive bypass means connected between one of the terina s of each of said potential drop producing devices and the negative terminal of the rectifier.

2. In a system of the character described, a series of thermionic devices arranged in succession to act upon electrical signaling impulses, each of said devices having a filament arranged to be heated to produce a stream of electrons, and a plate electrode, and means for supplying heating current to the filaments and a potential to each plate that is positive with respect to the filaments, comprising a rectifier for modifying commercial alternating current into rectified direct current, means connecting said rectifier in series with all of the filaments and plate electrodes, said connecting means including a potential drop producing device between each plate electrode and its electron emitting electrode, said drop producing devices being inductive to assist in reducing fluctuations in the series circuit, and capacitive by-pass means located at intervals along said series circuit and connected thereto between one terminal of the rectifier and the successive points of connection between each plate electrode and the potential drop producing devices connected therewith.

3. In a system of the character described, a series of electronic emission devices arranged in succession to act upon electrical signalling impulses, each of said devices having an electron emitting electrode and a plate electrode, and means for supplying a potential to the plate of each device that is positive with respect to the electron emitting device, comprising a rectifier for modifying commercial alternating current into rectified direct current, means connecting said rectifier in series with all of the plate electrodes and electron emitting electrodes, said connecting means including a potential drop producing device between each plate electrode and its electron emitting electrode, said drop producing devices being inductive to assist in reducing fiuctuations in the series circuit, and a plurality of capacitive by-pass means connected to said series circuit between one terminal of the rectifier and the plate terminal of each of said potential drop producing devices.

HAROLD F. ELLIOTT. 

